(1) Field of the Invention
The present invention relates generally to an intermediate cylinder for a sheet-fed press, and more particularly to an intermediate cylinder which is installed after a printing unit to adjust the traveling posture of a sheet being fed from the printing unit so that the sheet is stably conveyed. This invention also relates to a sheet-fed press with such an intermediate cylinder.
(2) Description of the Related Art
A wide variety of perfecting presses have lately been proposed and put to practical use.
FIG. 9 illustrates a perfecting press of a type where one-color printing is performed on both sides of a sheet 4. This press includes a reverse-side printing unit 1 disposed on the upstream side of a sheet traveling path along which the sheet 4 is traveled, and an obverse-side printing unit 2 disposed on the downstream side of the sheet traveling path.
In addition to the reverse-side printing unit 1 and the obverse-side printing unit 2, the sheet-fed press further includes a sheet feeder 19, a feeder board section 20, two intermediate cylinders 3a, 3b installed between the reverse-side printing unit 1 and the obverse-side printing unit 2 to convey the sheet 4 to the downstream side, a paper discharge unit 21, and so on.
The paper discharge unit 21 is constructed of a sheet conveyor 22, a sheet stacker 23 provided under the downstream end of the sheet conveyor 22, and so on.
The sheet feeder 19 is provided with a paper feed table 30 on which sheets 4 to be printed are stacked, and is operative to feed the uppermost sheet 4 in accordance with consumption speed (mechanical speed) when printing is performed. The sheet 4 fed by the sheet feeder 19 is conveyed by the feeder board section 20 to a first guide cylinder 24 disposed in the introducing portion of the reverse-side printing unit 1.
The sheet 4 is delivered from the first guide cylinder 24 to a second guide cylinder 25 and to the press cylinder 5a of the reverse-side printing unit 1, in which printing is performed on the reverse side of the sheet 4. Subsequently, the sheet 4 is conveyed by first and second intermediate cylinders 3a, 3b and delivered to the press cylinder 5b of the obverse printing unit 2, in which printing is performed on the obverse side of the sheet 4.
As shown in FIG. 11, the printing unit 2 (or 1) includes an ink reservoir 31, an ink roller group 32, a plate cylinder 34 with a printing plate 33 wound thereon, a blanket cylinder 35, a press cylinder 5, a wetter 36, and so on. The ink 18 supplied to the ink reservoir 31 is kneaded to the desired degree through the ink roller group 32 and transferred to the printing plate 33. The ink 18 is further transferred as an image to the outer peripheral surface of the blanket cylinder 35.
At the same time, wetting water is supplied to the blanket cylinder 35 from the wetter 36. Thereafter, the image transferred to the blanket cylinder 35 is transferred to the surface of the sheet 4 being traveled through the gap between the blanket cylinder 35 and the press cylinder 5. In this way, a predetermined printing is completed.
In FIG. 9, while the single reverse-side printing unit 1 and the single obverse-side printing unit 2 are shown, there is also a multiple color press in which a plurality of reverse-side printing units 1 and/or obverse-side printing units 2 differing in ink color are juxtaposed along the sheet traveling direction. In either case, the number of printing units 1, 2 is determined according to circumstances.
The printed sheet 4 is conveyed from the press cylinder 5b of the second printing unit 2 to the sheet conveyor 22 of the paper discharge unit 21. And the printed sheet 4 is gripped and conveyed onto the sheet stacker 23 by a chain gripper provided in an endless chain 28 being driven by a paper discharge shaft 27, and is stacked on the paper discharge table 29 of the sheet stacker 23. Subsequently, if a fixed quantity of sheets are stacked, then they are removed from the paper discharge table 29,
After printing is performed on the reverse side of the sheet 4, the ink 18 on the reverse side is dried at the outer peripheral surface of the second intermediate cylinder 3b by the first drier 17 disposed near the intermediate cylinder 3b. After printing is performed on the obverse side of the sheet 4, the ink 18 on the obverse side is dried by the second drier 17 when the sheet 4 is being gripped and conveyed by the gripper of the endless chain 22 which travels along the outer peripheral surface of the paper discharge shaft 27 from the press cylinder 5b. 
Most of the sheet-fed presses use ink that is dried and hardened by ultraviolet rays (UV). Therefore, UV driers for irradiating ultraviolet rays are often installed. However, it is desirable to install driers in accordance with the characteristics of ink used.
In the prior art sheet-fed press constructed as described above, the drying effect of the drier 17 is not sufficiently obtained at the second intermediate cylinder 3b which conveys the sheet 4 to the obverse-side printing unit 2 after printing is performed by the reverse-side printing unit 1. Because of this, poor drying such as uneven drying will occur, or the printing surface will be stained or scored.
The inventors have made various investigations and experiments and found that the above-described problems result mainly from flap of a sheet against an intermediate cylinder.
(1) The sheet 4 is conveyed with the front end gripped by the pawl member 26 of the intermediate cylinder 3. As shown in FIG. 10, means to control the posture of the sheet 4 is not present on the tail side of the sheet 4, and consequently, the sheet tail is free to move. Because of this, during conveyance, the sheet tail is separated from the surface (outer peripheral surface) of the intermediate cylinder 3 by the centrifugal force caused by rotation of the intermediate cylinder 3 and gravity. As a result, flap of the sheet 4 against the intermediate cylinder 3 is caused and the traveling posture of the sheet 4 becomes unstable.
(2) Because of the flap of the sheet 4 against the intermediate cylinder 3, the drying effect of the drier 17 is not sufficiently obtained and therefore there is a possibility that poor drying such as uneven drying will occur.
(3) If the sheet 4 is separated from the intermediate cylinder 3 because of centrifugal force, etc., the separated rear end portion will make contact with the drier 17, and consequently, the printing surface will be stained or scored.
(4) For the above-mentioned reasons, printing quality is considerably reduced and therefore there are cases where a great number of sheets are damaged.
In Japanese Utility Model Publication No. HEI 2-5951, there is disclosed a paper sending cylinder that sends a sheet to various cylinders on the downstream side while holding the sheet by suction. The paper sending cylinder is equipped with (1) an air tank provided in the cylinder end thereof, (2) a plurality of suction ducts held in fluid communication with the air tank and extending in the axial direction of the paper sending cylinder and provided so that they differ in phase in the circumferential direction, and (3) suction bores formed from the suction ducts to the outer peripheral surface of the paper sending cylinder. By actuating an external suction unit connected with the air tank, a sheet can be held on the outer peripheral surface of the paper sending cylinder by suction through the suction bores.
In the paper sending cylinder, shutter plates are inserted between the air tank and the suction ducts. A plurality of shutter plates are previously prepared. Each shutter plate has a through hole that is aligned with one of the suction ducts differing from one another. If a suitable shutter plate of the shutter plates is selected and used, a predetermined suction duct of the suction ducts provided so that they differ in phase in the circumferential direction can be selectively communicated with the air tank. In this way, the tail of the sheet can be held by suction through the suction bores formed at suitable positions in accordance with the size of the sheet.
In this technique, however, an operation of exchanging shutter plates must be performed each time a sheet of a different size is used. The shutter plate is inserted into a predetermined portion of the paper sending cylinder and is fastened with bolts. Thus, the exchanging operation is a troublesome operation involving time-consuming efforts.
The present invention overcomes the problems associated with the prior art. Accordingly, it is an object of the present invention to provide a sheet-fed press and an intermediate cylinder for a sheet-fed press that are capable of easily changing the settings of the press even if a sheet of a different size is used. Another object of the invention is to provide a sheet-fed press and an intermediate cylinder for a sheet-fed press which are capable of preventing poor drying and the occurrence of stains and scores in the printing surface by suppressing flap of a sheet against the intermediate cylinder which is to be described later.
In accordance with a form of the present invention, there is provided an intermediate cylinder that is used in a sheet-fed press to convey a sheet. The intermediate cylinder comprises a main body, a plurality of suction boxes formed in the main body at positions different with respect to a rotation axis of the main body (at different circumferential positions of the main body), and a plurality of suction bores formed on the suction boxes so that they are open at the outer peripheral surface of the main body. The intermediate cylinder further comprises suction force generation means for generating suction force within the suction boxes, and switching means for selectively switching connections between the plurality of suction boxes and the suction force generation means.
In accordance with another form of the present invention, there is provided a sheet-fed press including the above-described intermediate cylinder.
It has been found that providing suction boxes in a portion of the intermediate cylinder is effective to prevent flap of the sheet against the intermediate cylinder.
According to the intermediate cylinder and the sheet-fed press of the present invention, the sheet is held on the outer peripheral surface of the intermediate cylinder by suction, and consequently, flap of the sheet against the intermediate cylinder can be prevented. Therefore, in the case where the intermediate cylinder is disposed to face the drier, the drying effect of the drier is sufficiently obtained and poor drying such as uneven drying can be prevented. In addition, as contact between the sheet and drier is prevented, the printing surface can be prevented from being stained or scored.
Further in accordance with the present invention, connections between the suction boxes and the suction force generation means can be switched by the switching means, and the generation of suction force within the suction boxes disposed at different circumferential positions can be selected by the switching means. Therefore, to stably hold the sheet tail on the intermediate cylinder by suction, the operation of adjusting a position at which the sheet is held on the intermediate cylinder by suction can be easily performed by operation of the switching means.
In addition, it has been found that if a sheet-fed press is made by combining the above-described intermediate cylinder with the drier, the above-described problems can be greatly overcome. Moreover, it has been found that if the intermediate cylinder is provided with air jet means, the above-described problems can be more effectively overcome. The air jet means is operative to jet air so that the sheet delivered to the intermediate cylinder is stretched along the outer peripheral surface of the intermediate cylinder.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative example.